Lubricating grease containing metal salt of alpha-omega-dicarboxylic acids having molecular weights of about 500 to 2500

ABSTRACT

METAL SALTS OF BRANCHED CHAIN ALPHA-OMEGA-DICARBOXYLIC ACIDS HAVING MOLECULAR WEIGHTS OF ABOUT 500 TO 2500 ARE USEFUL IN LUBARICANTS, PARTICULARLY GREASES.

United States Patent LUBRICATING GREAE CONTAINING METAL SALT OF ALPHA-OMEGA-DICOXYLIC ACIDS HAVING MOLECULAR WEIGHTS OF ABOUT 500 TO 2500 Arnold J. Morway, Clark, N.J., Jeffrey H. Bartlett, Arlington, Va., and George R. Harrington, Baytown, Tex.,

assignors to Esso Research and Engineering Company No Drawing. Filed Apr. 1, 1968, Ser. No. 717,937 Int. Cl. Cm 3/18 US. Cl. 252-49 8 Claims ABSTRACT OF THE DISCLOSURE Metal salts of branched chain alpha-omega-dicarboxylic acids having molecular weights of about 500 to 2500 are useful in lubricants, particularly greases.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to lubricants containing metal salts of branched alpha-omega-dicarboxylic acids, such as carboxy terminated polyisobutylene, having molecular weights of about 500 to 2500.

DESCRIPTION OF THE PRIOR ART Polyisobutylene of about 40,000 to 200,000 molecular weight (Staudinger) has been used in gear lubricants and automotive chassis lubricants, primarily as an adhesiveness and stringiness agent, and to make non-spattering greases which are subject to shock loading. However, polyisobutylene of high molecular weight has poor shear stability and tends to break down and lose some of its adhesiveness as grease when it passes through the usual grease dispensing equipment. In general, the higher the molecular weight of polyisobutylene, the greater the stringiness it imparts, but the poorer its stability to shear breakdown. In addition, polyisobutylene per se will not gel oil to a solid and thus does not contribute significantly in thickening the oil to a more viscous composition, e.g. a grease.

SUMMARY OF THE INVENTION The salts of the branched carboxy-terminated dicarboxylic acids of the present invention, because of their shorter chains, are much more shear stable than the aforesaid polyisobutylene, yet are still capable of imparting adhesiveness and stringiness to a grease. At the same time, these salts per se are capable of thickening oil to a grease structure. Also, these salts can be used as a component of greases containing other thickeners, such as sodium soap grease where they tend to extend the high temperature lubrication life of the sodium soap greases. These salts can also be used with alkaline earth metal salt greases, such as calcium soap-salt greases, where they have a tendency to inhibit crust hardening that normally occurs when calcium mixed-salt greases are exposed to high temperatures. In addition, they can be used to advantage in inhibiting gelling of fluid or semi-fluid, alkaline earth metal mixed salt lubricants.

The lubricants of the invention will therefore comprise a major amount of lubricating oil, and about 1.0 to 30 wt. percent, preferably 3.0 to 8.0 wt. percent, of the branched alpha-omega dicarboxylic acid salt. If said dicarboxylic acid salt is used as the sole thickener, then generally about 10.0 to 30.0 wt. percent will give a solid grease structure. On the other hand, if used in combinations with other metal salt thickeners to form mixed-salt thickener systems, then .5 to 10.0 wt. percent of said dicarboxylic acid salt will generally be used.

The aforesaid mixed-salt thickener systems will usually be best made to contain alkali or alkaline earth metal salt of 1 to 25, preferably 2 to 15 wt. percent, of C to C fatty acid, preferably acetic acid. These systems may also contain metal salt of .5 to 20 Wt. percent, preferably 5 to 15 wt. percent, C to C preferably C to C fatty acid. Greases can be thus prepared having a total content of said salts of 10.0 to 49.0 weight percent, preferably 20 to 45 weight percent, based on the weight of the grease. These greases in turn can be diluted with additional oil to form fluid or semi-fluid compositions containing about 0.1 to 10.0 weight percent of the mixed salt. All of the aforesaid weight percents being based on the total weight of the final lubricant composition.

The alpha-omega-dicarboxylic acids, i.e. acids wherein the two carboxylic acid groups are at terminal ends of the molecule, namely the first carboxylic acid group is on the first carbon atom of the molecule While the second carboxylic acid group is on the terminal carbon atoms, used in the invention can have number average molecular weights as determined by high temperature osmometry of 500 to 2500, preferably 700 to 1500. These acids can be prepared by first forming an unsaturated polymer by copolymerization of a branched monoolefin with a diolefin. The resulting unsaturated polymer can then be treated to break the polymer at the double bonds and to form acid groups at the ends of the resulting polymer fragments, eg the unsaturated olefinic groups are ozonized, followed by their reduction to a carboxylic acid. Or the copolymers can be oxidized with oxidizing agents such as nitric acid to convert the olefinic groups to carboxylic acid groups and to break the original polymer chain. Or the olefinic groups can be hydroxylated to form vicinal glycols, followed by fusion of the glycols with caustic, such as sodium hydroxide or potassium hydroxides, at temperatures of 400 to 600 F.; for example as described in US. Pats.'2,801,971 and 2,801,977, to form dicarboxylic acid salts, which can be used per se, or which can be sprung by treatment with an inorganic metal acid, such as sulfuric acid to form the dicarboxylic acid.

The aforesaid unsaturated copolymer will generally be in the range of about 99 to 10, preferably 50 to 25 moles of C to C monoisoolefin such as isobutylene, 3-methyll-butene, and 4-methyl-l-pentene, per molar proportion of C to C conjugated diolefin wherein the second and third carbons are substituted only with hydrogen such as butadiene and piperylene.

The copolymerization of the mono and diolefin Will generally be carried out at a low temperature, e.g. between about 50 and l65 C. or lower in the presence of a Friedel-Crafts catalyst such as aluminum tribromide, aluminum trichloride, etc., in a solvent such as a lower alkyl halide, e.g. methyl chloride or ethyl chloride. US. Pat. 2,356,128 illustrates this reaction and fully describes the methods for the preparation of isobutylenediolefin copolymers. The final rubbery polymer generally has a viscosity average molecular weight (in diisobutylene) of between about 100,000 and about 1,- 500,000 and a degree of unsaturation characterized by a Wijs iodine No. of between about 5 and about 50, usually between about 15 and about 50.

While, as previously indicated, several different ways can be utilized to break the polymer at its double bonds and form carboxylic acid groups, the specific technique in preparing the dicarboxylic acid used in the working examples was by ozonolysis. Ozonolysis can be carried out by first dissolving about 1 to 30 wt. percent, preferably 10 to 20 wt. percent, copolymer in a suitable solvent, e.g. an aliphatic hydrocarbon as pentane, hexane, heptane, chloroform, etc. to form a cement. The actual ozonolysis itself can be carried out at temperatures between 80 C. and +60 0., preferably -25 C. to +40 C. and pressures of atmospheric up to 500 p.s.i.g. or more. Pyridine, or substituted pyridine, for example C to C alkyl substituted pyridines, quinolines, isoquinolines, pyridine homologs, etc., in an amount of .25 to 10 moles, preferably 1 to 5 moles, per mole of starting olefin, is added to the aforesaid cement, preferably before the start of the ozonization reaction.

The ozonization is carried out by bubbling air or oxygen containing .1% to 50%, preferably 1 to wt. percent ozone, through the solution of solvent copolymerpyridine, using about 1.3 to 3.0 moles ozone per mole of original unsaturation, preferably 1.52.5 moles 0 mole double bond. During ozonization, a peracid is formed which is subsequently reduced to the carboxylic group, either by storage or heating with or without pyridine present, although reduction can also be carried out by treating the peracid with alkyl or aryl amines, phosphines, organic sulfides, thiols, and organic phosphites. However, heat reduction is preferred. Excess reducing agent and its oxidation products are usually, but not always, removed after the reduction either by contacting with acidic resins (Amberlyst, Dowex) or by water or dilute acid washing. In cases where the oxidized reducing agents form products insoluble in organic solvents, they can be separated from the polymer solution by filtration. The polymeric diacids are recovered from the aliphatic solvents by stripping the solvent followed by vacuum drying.

The reactions during ozonolysis can be represented as follows:

First stage ozonolysis R-COOH R-CH=O Second stage ozonolysis The ozone is contacted with the polymer until unreacted ozone is detected. The turning of a potassium iodide solution to a deep reddish brown color, or the breakage of a stretched unvulcanized natural rubber band due to attack on the double bonds present, can be used to detect the breakthrough of unreacted ozone, indicating the end of the first stage. Additional ozone is added in the second stage to oxidize residual aldehyde groups. Ozonolysis in the second stage is continued for a time of about 10 to 500% of the time necessary for the first stage ozonolysis or until no additional acid build-up occurs which can be readily detected by titration.

The metal component of the dicarboxylic acids can be any of the common grease making metals including alkali metal such as sodium, lithium; alkaline earth metal such as calcium, barium, magnesium, strontium; iron, aluminum, etc. These metals will usually be reacted in the form of their bases, i.e. hydroxides, carbonates or oxides, with the diearboxylic acid, preferably dispersed in at least a portion of the lubricating oil.

As indicated earlier, these dicarboxylic acids can be used to form various mixed salt greases, preferably by coneutralizing the dicarboxylic acid in various combinations with low, intermediate and high molecular weight fatty acids.

The low molecular weight fatty acids are preferably those of 2 to 4 carbon atoms and include acetic, propionic, n-butyric, etc. Acetic acid or its anhydride is preferred.

Intermediate molecular weight fatty acids include thOse aliphatic, saturated, unsubstituted, monocarboxylic acids containing 7 to 12 carbon atoms per molecule, e.g. capric, lauric, caprylic, nonanoic acid, etc.

The high molecular weight fatty acids useful for forming the mixed-salt thickeners include naturally-occurring or synthetic, hydroxy substituted and unsubstituted, saturated and unsaturated, mixed or unmixed fatty acids having about 13 to 30, preferably 16 to 22, carbon atoms per molecule. Examples of such acids include stearic, hydroxy stearic, such as 12-hydroxy stearic, dihydroxy stearic, polyhydroxy stearic and other saturated hydroxy fatty acids, arachidic, oleic, ricinoleic, hydrogenated fish oil, tallow acids, etc.

The lubricating oil used in the compositions of the invention can be either a mineral lubricating oil or a synthetic lubricating oil. Synthetic lubricating oils which may be used include polyphenyl ether oils, polysilicone oils, esters of dibasic acids (e.g. di-2-ethylhexyl sebacate), esters of glycols (e.g. C Oxo acid diester of tetraethylene glycol), complex esters (eg the complex ester formed by reacting one mole of sebacic acid with two moles of tetraethylene glycol and two moles of Z-ethyl-hexanoic acid), halo-carbon oils, alkyl silicates, sulfite esters, mercaptals, formals, polyglycol type synthetic oils, etc. or mixtures of any of the above in any proportion.

Various other additives may also be added to the lubrieating composition (e.g. 0.1 to 10.0 weight percent each, based on the total weight of the composition). Such additives include oxidation inhibitors such as phenyl-alphanaphthylarnine, phenothiazine and dioctyldiphenylamine; corrosion inhibitors such as sodium nitrite and sorbitan monooleate; supplemental grease thickeners such as polyethylene and polypropylene; stabilizers such as aluminum hydroxy stearate, dispersants such as phosphorsulfurized polyisobutylene, and the like.

The compositions of the invention may be prepared in several ways. In one method, the dicarboxylic acid, together with any fatty acid being used, is dispersed in the base oil and neutralized with the metal base. The water of reaction may be left in the lubricant by not applying heat to thereby form a cold-set lubricant. However, generally the product will be heated to about 225 to 600 F. to dehydrate the mixture. If dehydrated at 225 F. to 400 F. the resulting composition will usually be less thick, at least if it is a calcium grease, than if higher dehydration temperatures are used. This 225 to 400 F. dehydration technique is advantageously used in making semi-fluid or soft calcium greases. If a calcium mixed salt composition is heated above 400 F., say about 430 to 600 F., then a pronounced thickening effect usually occurs which can be used to advantage when a more solid or a harder product is desired.

In each of the above cases involving heating, the mixture may then be next cooled to about to 350 R, where conventional additives, if any, may be added. The grease is then preferably cooled to below F. where it may be homogenized, as by passing through a Gaulin homogenizer or 21 Charlotte mill, followed by subsequent cooling to room temperature. If desired, grease concentrates can be made by the above techniques and then diluted with additional lubricating oil to form the final grease composition or even further diluted to form fluid or semi-fluid lubricants.

The invention will be further understood by the following examples, wherein all parts are by weight.

5 PREPARATION OF ALPHA-OMEGA DICARBOX- YLIC ACID-PREPARATION A A stirred, jacketed reactor was charged with 1500 ml. of a hexane solution consisting of 10 gm. of copolymer per 100 gm. of hexane. The copolymer consisted of 97.1 mole percent isobutylene and 2.9 mol percent piperylene, said copolymer having an Sil. 350.15 iodine number of 19.4 gm. iodine per 100 gm. copolymer and a viscosity average molecular weight (in diisobutylene) of 298,000. To this solution 5.5 ml. of pyridine was initially added and the contents chilled to +4 C. A stream of oxygen containing 26.6 mg. per liter of gas was bubbled through the solution at the rate of 3 liters of gas per minute, or 79.8 mg. 0 per min. At the end of 25 minutes, an additional 4.1 ml. of pyridine was added, and after the end of 50 minutes from the start of ozone addition, another 4.1 ml. of pyridine was added. At the end of 81 minutes from the start of ozone addition, ozone breakthrough occurred as indicated by breakage of an unvulcanizeid natural rubber band. The second stage addition was then started while maintaining the temperature of +4 C., using a concentration of 36 mg. 0 per liter of oxygen, adding the gas at the rate of 2 liters per min. or 72.0 mg. 0 per min. for 60 minutes, at which point the second stage was indicated as completed by no further build-up of acids as indicated by periodic titration of samples of the reaction product being formed dissolved in MIBK (methyl isobutyl ketone) as solvent.

The reaction product containing the alpha-omega dicarboxylic acid was then finished by stripping oh. the hexane on a steam bath, which also simultaneously decomposed the peracid, followed by vacuum drying at 90 C. for 16 hours in a vacuum oven operating at about 5 mm. Hg pressure. The insoluble pyridine oxide was removed by redissolving the remaining reaction product in pentane, filtering through a paper filter, and then stripping the pentane on a steam bath, followed by again vacuum drying for 16 hours at 90 C. under a pressure of 5 mm. Hg.

The resulting purified alpha-omega dicarboxylic acid had a MIBK acid number of 47.7 mg. KOH/gm. and a number average molecular weight (Mn) of 1755 as determined by high temperature osmometry.

PREPARATION B AND 0 These preparations were prepared in the same manner as Preparation A, except for some variation in the ozone addition.

The conditions under which Preparations A to C were carried out are summarized in the following table:

TABLE I.-PREPARATION OF ALPHA-OMEGA DICARBOX- YLIC ACID Preparation A B 0 Base polymer used in ozonolysis:

Mv (in diisobutylene) 298, 000 298, 000 208, 000 INOPO gm. iodine/100 g. pol 19. 4 19 19. 4 Reaction temp., C +4 +4 Initial charge, m1 1, 500 1, 500 1, 500 Concentration, polymer/n-hexane,

gm./cc /100 /100 15/100 Pyridine addition:

MiuJmL Min. /ml Min./ml 1 First stage:

Mg. O /liter 26. 6 26. 6 26. 6 Liter/min 3. 0 3. 0 3. 0 Mg. O /min 79. 8 79. 6 79. 6 Time ozone breakthrough, min. 81 110 113 Second stage:

Mg. O /liter 36.0 36.0 36.0 Liter/min 2. 0 2. 0 2. 0 Mg. 0 /111111 72. 0 72. 0 72. 0 Time 60 60 60 Analysis:

MIBK acid No., mg. KOI-I/g 47. 7 50. 3 67.5 n 1, 755 I, 923 1, 853

6 PREPARATION D Portions of the acid from each of the Preparations A, B, and C were mixed together in the following amounts: 89.3 gm. of Preparation A, 153.4 gm. of Preparation B, and 168 gm. of Preparation C. This mixture had a neutralization number of 48.3 mg. KOH/gm, a saponification number of 86.9 mg. KOH/gm., an average viscosity mol. wt. of 1873, and a MIBK acid No. of 47 mg. KOH/gm. This mixture of acid contained essentially alpha-omega polyisobutylene dicarboxylic acid and very minor amounts of mono and tricarboxylic acids.

The above mixture of acids were used in the following examples wherein all parts are by weight.

EXAMPLE I A grease composition was prepared as follows:

15 parts of tallow fatty acids having a saponification number of 195 and a Wijs iodine number of 55; 4 parts of the polyisobutylene dicarboxylic acid mixture of Preparation D; and 60 parts of mineral lubricating oil having a viscosity of 60 SUS at 210 F., were added to an electrically heated grease kettle and warmed to about 100 P. Then, 10 parts of glacial acetic acid was added over about /2 hour, to the kettle while stirring. Then 9 parts of sodium hydroxide (100%) was added in the form of an aqueous solution consisting of 40 wt. percent NaOH and 60 wt. percent water. The resulting mixture was then heated while stirring to about 420 R, which temperature was maintained for about 30 minutes to completely evaporate the water of reaction and dehydrate the grease. The heat was then turned off and the grease was then allowed to cool to about 300 F., while stirring, where 1 part of phenylalpha-uaphthylamine was added as an antioxidant. The grease was allowed to cool to 125 F. and then homogenized by passage through a Morehouse mill having an opening of about .002 inch.

EXAMPLE II The procedure of Example I was followed except that the proportion of ingredients was changed and Hydrofol acid 51 was used in place of the tallow fatty acids.

Hydrofol acid 51 is hydrogenated fish oil acid averaging about C and having a degree of unsaturation similar to oleic acid.

EXAMPLE III This grease was prepared in a manner similar to that of Example I except: Hydrofol acid 51 was used in place of tallow acid; a solution of 20 wt. percent LiOH-monohydrate in wt. percent water was used in place of the sodium hydroxide solution, and after the grease was cooled to about 125 F. and prior to passage through the Morehouse mill, 3 parts of a 50/50 mixture by weight of finely divided sodium nitrite dispersed in mineral lubricating oil was added to the grease as a rust preventative.

EXAMPLE IV 88 parts of mineral lubricating oil having a viscosity of 60 SUS at 210 F. and 10 parts of the dicarboxylic acid of Preparation D were charged to a gas-fired grease kettle and warmed to about 125 F. Then 1 part of sodium hydroxide in the form of an aqueous solution consisting of 40% sodium hydroxide and 60% water was added to the kettle. The kettle contents were heated to 400 F. until all the water had evaporated and the resulting dehydrated grease was then cooled rapidly to about F. where 1 part of the phenyl-alpha-naphthylamine was added as antioxidant. The grease was then passed through a Morehouse mill having a clearance of about .002".

EXAMPLE V Example IV was repeated except that lithium hydroxide monohydrate was used in place of the sodium hydroxide. The compositions and properties of the greases of EX- amples I to V are summarized in the following Table II:

TABLE II Formulated (wt. percent): Glacial acetic acid. Tallow fatty acids. Hydrofol acid 51 Alpha-omega diearboxylic acid Sodium hydroxide LiOH. H2O Ihenyl-alpha-naphthylamine 50/50 sodium nitrite in oil Mineral lubricating oil of 60 SUS at 210 Molar hydrogen equivalent ratio acetic/dicarb. acid.

Molar hydrogen equivalent ratio high fatty acid/dicarb. acid 12/1 12/1 16/1 Properties:

Appearance Excellent smooth homogeneous greases Dropping point, F 400+ 400+ 400+ 35 350 ASTM penetrations, 77 F. min/:

Unworkcd r 180 280 295 340 310 Worked 60 strokes 00 285 300 360 360 Worked 10,000 strokes. 200 330 310 Water resistance 2 (1) 2 Bearing protection, ASTM 14 day rust test Lubrication life, NLGI-ABEC, hours at 10,000 rpm. at 300 F. 890

Adhesiveness Stringiness. Shear breakdown Crust hardening- Adhesive and cohesive Mo crate Good resistance to shear Shows no tendency to crust harden Soluble. Insoluble. Pass.

As seen by the data in Table II all of the greases containing the branched chain alpha-omega dicarboxylic acids were adhesive and cohesive, had moderate stringiness, and had good resistance to shear. Examples I to III show how the alpha-omega dicarboxylic acid can be used as a minor component in mixed salt thickened greases in order to impart adhesiveness and cohesiveness to the greases. Greases similar to those of Examples I to III, but without the alpha-omega dicarboxylic acid component, did not have these adhesiveness, cohesiveness and stringiness properties. Examples IV and V show how the high molecular weight alpha-omega dicarboxylic acid can be used as the sole grease thickener.

EXAMPLE VI A viscous fluid lubricant suitable for lubrication of the upper cylinders of marine diesel engines was prepared as follows:

52.32 parts of mineral lubricating oil having a viscosity of 80 SUS at 210 F., 3.46 parts of tallow fatty acid, 5.12 parts of an oil solution consisting of 30 wt. percent mineral lubricating oil and wt. percent of 9. P 5 treated polyisobutylene of 1800 molecular weight, 2.48 parts of the dicarboxylic acid of Preparation D, and 14.14 parts of hydrated lime, were mixed together in a steam jacketed grease kettle. Then 22.18 parts of glacial acetic acid was slowly added while mixing and keeping the temperature of the kettle contents below about 125 F. The resulting grease mixture was then heated to 300 F. in order to dehydrate said mixture. The product was next cooled to 250 R, where 0.26 part of phenyl-alpha-naphthylamine was added, and was then further cooled to room temperature to form a grease-like concentrate. Mixing was carried out during the entire process described above by cycling the kettle contents through a Charlotte colloidal mill and then back to the kettle.

The P S polyisobutylene used above was prepared by reacting a polyisobutylene of about 1800 molecular weight (Staudinger) with 15 wt. percent P 5 based on the weight of polyisobutylene, at about 425 'F. for about 8 hours under a nitrogen atmosphere.

18.5 parts of the aforesaid grease-like concentrate was mixed with 81.5 parts of additional mineral oil of 80 SUS viscosity at 210 F. to thereby form a fluid diesel engine cylinder lubricant. A sample of this semi-fluid lubricant was held in an oven at 370 F. at about 4 hours and then examined and was found to be fluid and without a hard crust. A similar lubricant prepared in the same way but without the branched chain alpha-omega dicarboxylic acid forms a hard crust when heated at 370 F. for 4 hours.

What is claimed is:

1. A lubricant comprising a major amount of lubricat ing oil, and about 1 to 30 wt. percent, based on the weight of the total composition, of metal salt of branched chain aliphatic saturated alpha-omega dicarboxylic acid wherein said carboxylic acid groups are on terminal carbon atoms of said molecule having a molecular weight of about 500 to 2500 obtained from an unsaturated copolymer of about 100,000 to 1,500,000 molecular weight of 99 to 10 molar proportions of C to C monoisoolefin per molar proportion of a C to C conjugated diolefin whose second and third carbon atoms are substituted only with hydrogen, by breaking said copolymer at its unsaturation points and forming carboxylic acid groups.

2. A lubricant according to claim 1, wherein said copolymer is a copolymer of isobutylene and piperylene.

3. A lubricant according to claim 1, wherein said metal is alkali metal and said oil is mineral lubricating oil.

4. A lubricant according to claim 3, wherein said lubricant contains 10 to 30 wt. percent of alkali metal salt of said dicarboxylic acid as the sole thickener in said lubricant.

5. A lubricating grease comprising a major amount of a mineral lubricating oil, and about 5 to 49 wt. percent of a metal mixed salt thickener of 1 to 25 wt. percent C to C fatty acid, 0.5 to 20 wt. percent of C to C fatty acid, and 0.5 to 10.0 wt. percent of branched chain aliphatic saturated alpha-omega dicarboxylic acid wherein said dicarboxylic acid groups are on terminal carbon atoms of said molecule of 500 to 2500 mol. wt. obtained from an unsaturated copolymer of about 100,000 to 1,500,000 molecular weight of 99 to 10 molar proportions of C to C monoisoolefin per molar proportion of a C to C conjugated diolefin whose second and third carbon atoms are substituted only with hydrogen, by breaking said copolymer at its unsaturation points and forming acid groups.

6. A lubricating grease according to claim 5, wherein said metal is selected from the group consisting of alkali metal and alkaline earth metal, said C to C fatty acid is acetic acid, and said dicarboxylic acid is obtained by ozonolysis and reduction of a copolymer of about 97 mole percent isobutylene and about 3 mole percent piperylene having a molecular weight of about 300,000.

7. A lubricating grease according to claim 5, wherein said metal is alkali metal.

8. A lubricating grease according to claim 5, wherein 3,216,937 11/1965 Morway et a1. 252-39 said metal is alkaline earth metal. 3,234,130 2/ 1966 Nixon et a1 25239 3,314,886 4/1967 Morway et a1 252-39 References Cited DANIEL E. WYMAN, Primary Examiner UNITED STATES PATENTS 5 I 2,801,971 8/1957 Bartlett et a1. 2s2 41 L VAUGHN Asslstant Exammer 2,801,977 8/1957 Morway et a1 252-41 US. Cl, X.R,

2,898,296 8/1959 Pattenden et a1. 25239 252-35, 36, 40, 41 

